1. Technical Field
This invention relates to fluid flow meters utilizing ultrasonic sensors on pipe walls in general, and to the same which use a gel form ultrasonic couplant disposed between the sensor and the pipe wall in particular.
2. Background Information
Clamp-on ultrasonic flow meters are a desirable tool for determining characteristics of a fluid flow traveling through a pipe. Ultrasonic flow meters typically include a plurality of ultrasonic sensors, each having a transmitter and a receiver. In some sensor configurations, ultrasonic signals emitted from the transmitters travel through the immediate pipe wall, the fluid flow disposed within the pipe, and through the opposite pipe wall where they are sensed by the receiver portion. In other sensor configurations, the transmitters and receivers are disposed on the same side of the pipe; the sensed fluid flow signal component is one that has reflected off of the opposite pipe wall and traversed the fluid flow a second time. Regardless of the sensor configuration, the received signal is processed to determine information such as flow velocity, volumetric flow rate, water cut, etc.
It is known to use an acoustic couplant disposed between the pipe wall and one or both of the transmitter and receiver of each sensor. The couplant provides a lower impedance signal path between the pipe and the sensor component and thereby enhances the ability of the sensor to transmit and receive ultrasonic signals.
One of the problems with using a couplant is that it may degrade or migrate away from the interface between the sensor and the pipe surface over time, thereby compromising the performance of the sensor. This is particularly true in applications where the sensors and the couplant are subject to harsh environmental conditions such as large temperature and or humidity variances, exposure to sunlight, and exposure to contaminants (e.g., sand, oil, dirt, etc.). Consequently, there is a need to provide a means for ensuring that a couplant disposed between a sensor and a pipe surface will remain intact and operable without being compromised.